Short answer: Large doses are the concern. The NIH Office of Dietary Supplements says vitamin E can slow platelet clumping and work against vitamin K clotting factors, so large doses taken with an anticoagulant or antiplatelet medicine such as warfarin can raise bleeding risk. It says the amount needed is unknown but probably above 400 IU a day. Vitamin E from food has no reported harms. Check with your prescriber before adding a supplement.
The NIH Office of Dietary Supplements (ODS) vitamin E fact sheet lists anticoagulant and antiplatelet medicines as interactions. It says vitamin E can inhibit platelet aggregation (the clumping that starts a clot) and antagonize vitamin K-dependent clotting factors. As a result, taking large doses of vitamin E with these medicines, such as warfarin, can increase the risk of bleeding, especially when vitamin K intake is low.
It adds that the amount of supplemental vitamin E needed to produce clinically significant effects is unknown but probably exceeds 400 IU a day. The fact sheet names warfarin as its example and does not give separate guidance for each newer blood thinner.
| Measure | Amount |
|---|---|
| Recommended daily amount (adults 19+) | 15 mg (19 mg when breastfeeding) |
| Upper limit from supplements (adults) | 1,000 mg, equal to 1,500 IU natural or 1,100 IU synthetic |
| Level where blood-thinner effects probably start | Above 400 IU a day (exact amount unknown) |
Supplement labels may list vitamin E in mg or IU. The ODS says 1 mg of vitamin E equals 1 mg of natural (d-alpha) tocopherol or 2 mg of synthetic (dl-alpha) tocopherol, so the same number of milligrams on a synthetic product delivers less. The upper limit was set for the general public based on bleeding effects; it is not a safe amount for someone on a blood thinner.
The ODS says high-dose vitamin E has caused bleeding and interrupted clotting in animals, and that two clinical trials found more hemorrhagic (bleeding) strokes in people taking it. One was in Finnish men who smoked and took 50 mg a day for about 6 years. The other was the Physicians' Health Study II.
In that trial, 14,641 US male doctors aged 50 and older took 400 IU of vitamin E every other day or placebo for about 8 years. Vitamin E did not lower heart attacks, strokes overall or heart deaths, but it was linked to more hemorrhagic strokes (hazard ratio 1.74). The ODS notes that most of these doctors also took aspirin, which could point to a bleeding tendency with vitamin E.
MedlinePlus tells people on warfarin to tell their doctor and pharmacist about all vitamins and supplements, because some may raise bleeding risk. MedlinePlus lists easy bruising, nosebleeds, bleeding gums and bleeding that will not stop among the signs to report right away. A pharmacist can also check how much vitamin E is in each product you take.
For related interactions, see vitamin K and warfarin and fish oil and blood thinners. Dose Track keeps your medicines and supplements in one list, which makes the pharmacist check quicker.
Read more on Dose Track: Interaction checker · Fish oil vs krill oil · What counts as a dietary supplement? · Orlistat and fat-soluble vitamins